Grain Boundary Segregation of Sulfur, Nitrogen, and Carbon in α‐Iron

The segregation of sulfur, nitrogen, and carbon at surfaces and grain boundaries of α‐iron was studied by Auger Electron Spectroscopy (AES). Specimens of pure iron, doped with nitrogen or carbon by equilibria with gas mixtures were introduced into the UHV‐chamber and fractured by impact at about −130°C. Enrichment of nitrogen, carbon, or sulfur was observed on the intergranular fracture surfaces. Displacement equilibria exist between nitrogen or carbon and sulfur, which was present in the bulk material only as a trace impurity. The presence of sulfur decreases the cohesion of the grain boundaries, so that mainly intergranular fracture occurs. Obviously nitrogen or carbon reinforce the cohesion of grain boundaries, so that transgranular fracture prevails.